High pressure sodium lamps employing polycrystalline alumina arc tubes having tungsten electrodes at either end thereof are known, see, for example, U.S. Pat. No. 4,545,799. Such electrodes often employ electron emissive materials such as barium, strontium, calcium, yttrium, tungsten or mixtures thereof. During lamp operation these materials are sputtered from the electrodes and deposit on the interior of the arc tube envelope, leaving a black coating thereon which can increase the emissivity of the arc tube and decrease the wall temperature. These effects lead to a lowering of the lamp efficacy. Additionally, the use of electrodes can lead to cracking of the material due to the expansion differences between the metal and ceramic.